Enhanced concentration of ammonium salt fertilizer extracted from biogas effluent

Abstract

Embodiments disclosed herein are directed to methods and systems of concentrating ammonium salt brine extracted as ammonia from mechanically filtered biogas effluent. The mechanically filtered biogas effluent is post-treated with micro-nano- bubblers, coagulants, and / or flocculants, alone or in combination, to remove contaminants. The treated biogas effluent is fed into, and processed through, a system of forward osmosis membrane filtration devices. Ammonia is at least partially removed from the treated biogas effluent, drawn across one or more forward osmosis membranes and into the forward osmosis draw solution where it is converted to ammonium salt and subsequently concentrated via reverse osmosis. The reverse osmosis retentate brine is separated into two streams: a draw solution stream to be replenished with acid before being recirculated and an ammonium salt brine stream. The ammonium salt brine stream is treated by an osmotically assisted reverse osmosis membrane system to further concentrate the ammonium brine stream.

Description

38511.0028P1ENHANCED CONCENTRATION OF AMMONIUM SALT FERTILIZEREXTRACTED FROM BIOGAS EFFLUENTBACKGROUND

[0001] Filtered digester effluent from biomass digesters can be processed to extract various salts and minerals as disclosed in US Patent Application Number 16 / 461.081, published as US2020 / 0061541, which is incorporated herein, in its entirely, by this reference. Of particular interest are the ammonium salts which are valuable for use as fertilizer, preferably organic fertilizer and more preferably certified organic fertilizer. Ammonia and water from the filtered digester effluent pass through an ammonia- permeable forward osmosis filtration system membrane and the permeate is captured in the draw solution of the forward osmosis filtration system. The draw solution is acidic, causing the ammonia captured in the draw solution to convert to ammonium cations, which have relatively limited permeability' back through the forward osmosis membrane. Ammonium ions in the diluted draw solution combined with the acid produces one or more ammonium salts. The diluted draw solution becomes an ammonium brine stream that is then dewatered via reverse osmosis, thereby concentrating the retentate ammonium brine stream, to about 16% for ammonium sulfate. Part of the ammonium brine stream is recirculated, with the addition of more acid, as reconstituted draw solution before it is applied to the permeate side of the forward osmosis membrane.

[0002] Laboratory testing has shown that the filtered digester effluent from biomass digesters contains molecules, such as, but not limited to, lignins, mucus, proteins, and protein fragments, that are difficult to mechanically remove and may form gels in the biogas effluent and in the forward osmosis filtration devices. The presence of these gels impacts the ability of the forward osmosis filtration system to efficiently, effectively, and consistently draw ammonia across the forward osmosis membranes and into the draw solutions. The presence of these molecules in the biogas effluent stream that is fed into the forward osmosis membrane filtration system challenges the overall viability- of the system for cost effectively producing ammonium salt fertilizer.

[0003] Continued processing of the brine stream can also include forward osmosis membrane crystallization of the ammonium brine such as disclosed in PCT / US Patent Application PCT / US2024 / 020562.38511.0028P1SUMMARY

[0004] Embodiments disclosed herein are directed to methods and systems for enhancing the concentration of ammonium salt fertilizer extracted from biogas effluent. Enhancements include, but are not limited to, using an osmotically assisted reverse osmosis (OARO) system to further concentrate the ammonium salt brine stream, incorporating a micro-nano-bubbler to remove gel forming impurities in the biogas effluent stream, and using a flocculant and / or coagulant to remove gel forming impurities in the biogas effluent stream.

[0005] In an embodiment, the OARO system increases the concentration of the ammonium salt brine stream, from about 16% to about 33% salinitv for ammonium sulfate.

[0006] In an embodiment, the OARO system approximately doubles the concentration of the ammonium salt brine stream.

[0007] In an embodiment, the OARO system increases the relative concentration of the ammonium salt brine stream by around 10-50% (1. 1-1.5 times), by around 50- 100% (1.5-2 times), or by over 100% compared to the concentration of the OARO feed stream.

[0008] In an embodiment, the flocculant and / or coagulant is used for separation and removal of molecules that can form gels including, but not limited to, one or more of lignins, mucus, proteins and peptides, as well other contaminants, from the mechanically filtered biogas stream. This has the advantage providing stable operation of a forward osmosis (FO) system which is otherwise compromised when these molecules gel within the FO modules.

[0009] In an embodiment, the micro-bubbler and / or nano-bubbler is used with the flocculant and / or coagulant to increase the efficiency of separation and removal of molecules that can form gels including, but not limited to, one or more of lignins, mucus, proteins and peptides, as well other contaminants, from the mechanically filtered biogas effluent stream. This has the advantage providing stable operation of the FO which is otherwise compromised when these molecules gel within the FO modules. The bubbler and / or flocculants and / or coagulant may remove other contaminants not removed during mechanical filtration.38511.0028P1

[0010] In an embodiment, the flocculant and / or coagulant is incorporated into the filtered biogas effluent and subsequently skimmed off or otherwise removed or isolated from the filtered biogas effluent before being fed into the FO system.

[0011] In one or more embodiments, the flocculant and / or coagulant is made of a non-organically certified material or materials.

[0012] In one or more embodiments, the forward osmosis membrane prevents passage through the membrane of any materials, from the biogas effluent or from processing of the biogas effluent, that would prevent organic certification of the ammonium salt.

[0013] In an embodiment, no polymer in the flocculant and / or coagulant crosses the FO membrane. This ensures the purity of the ammonium salt fertilizer produced allowing the use of non-organic certified polymers as the flocculant and / or coagulant.

[0014] In an embodiment, the flocculant combines with smaller molecules that are potentially gel forming impurities in the mechanically filtered biogas digestate. The larger combined particles can be removed from the mechanically filtered biogas digestate such as by, but not limited to, gravity separation, filtration, and / or vacuum. Coagulants may be used to neutralize charges on particles and flocculants bind the neutralized particles together.

[0015] In one or more embodiments, the ammonium salt concentration sy stem for biogas effluent includes a forward osmosis membrane brine crystallizer after the OARO system.

[0016] In an embodiment, a method of producing concentrated ammonium salt fertilizer from filtered biogas digestate effluent is disclosed. The method includes using one or more flocculants and / or coagulant and micro bubblers or nano bubblers to remove potential gel forming molecules from the filtered biogas digestate effluent, thereby creating or producing a treated biogas effluent. The treated biogas effluent is input to the feed side of at last one forward osmosis filter having a draw solution that is acidic and draws or transfers ammonia and water across the filter where the ammonia is converted to ammonium cations, creating an ammonium brine stream that is subsequently concentrated by reverse osmosis. The method may include further concentration of a portion of the RO retentate ammonium brine stream by OARO such that the relative concentration of the ammonium brine stream increases by around 10-50% (1.1-1.5 times), by around 50-100% (1.5-2 times), or by over 100% compared to the concentration of the OARO feed stream.38511.0028P1The method may include further processing of the OARO retentate ammonium brine stream using a forward osmosis membrane brine crystallizer.

[0017] In one or more embodiments, an organically certified ammonium salt, said ammonium salt produced from biogas effluent where the biogas effluent is treated with non-organic flocculant and / or coagulant. The ammonia in the treated biogas effluent is extracted by a forward osmosis filtration unit thereby eliminating any non-organic materials from the flocculant and / or coagulant from contaminating the final produced ammonium salt.

[0018] Features from any of the disclosed embodiments may be used in combination with one another, without limitation. In addition, other features and advantages of the present disclosure will become apparent to those of ordinary skill in the art through consideration of the following detailed description and the accompanying drawings.BRIEF DESCRIPTION OF THE DRAWINGS

[0019] The drawings illustrate several embodiments of the present disclosure, wherein identical reference numerals refer to identical or similar elements or features in different views or embodiments shown in the drawings.

[0020] FIG. l is a schematic view of a prior art method of concentrating digestate from biomass, according to an embodiment.

[0021] FIG. 2 is a schematic of view of the forward osmosis system portion of FIG. 1 with the addition of an osmotically assisted reverse osmosis system, a micro-bubbler system, and a flocculant and / or coagulant.DETAILED DESCRIPTION

[0022] Embodiments disclosed herein are directed to methods and systems for treating mechanically filtered biogas effluent from a biomass digester to remove potential contaminants prior to subsequent forw ard osmosis membrane filtration; transferring ammonia from the biogas effluent across the forward osmosis membrane to a draw solution; and employing reverse osmosis and osmotically assisted reverse osmosis systems to create a concentrated ammonium salt brine fertilizer, which may then be crystallized in a forward osmosis membrane crystallizer.38511.0028P1

[0023] Additional membrane-based concentration of the ammonium brine stream produced from biogas effluent would be beneficial in reducing the volume of the brine and the associated costs of storage, handling, and transportation as well as reducing energy and capital costs associated with thermal evaporation equipment.

[0024] FIG. 1 shows the system as detailed in U.S. Patent Application Number 16 / 461.081. For example, embodiments of a method of concentrating digestate from biomass are disclosed in U.S. Patent Application No. 16 / 461,081 filed November 16. 2017, the disclosure of each of which is incorporated herein, in its entirety, by this reference. Aspects of the present disclosure includes the system shown in FIG. 2. In many embodiments, new elements for the new ammonium salt fertilizer producing system 300 are incorporated based on new insights to improve the viability and value of producing ammonium salt fertilizer 388 from mechanically filtered biogas digestate 308 compared to the system of FIG. 1. The new ammonium fertilizer salt producing system 300 produces a treated biogas effluent 338 from the mechanically filtered biogas digestate 308 to enhance the quality of the feed into the forward osmosis system, preventing gel formations which, through laboratory experimentation, have been demonstrated to clog or partially clog the forward osmosis filter, reducing efficiency and effectiveness and increasing the cost of producing ammonium salts. The new ammonium fertilizer salt producing system 300 also includes an osmotically assisted reverse osmosis system 380 that can approximately double the concentration of the ammonium salt fertilizer produced, from about 1 % salinity to about 33% salinity for ammonium sulfate, based on experimental results. This osmotically assisted reverse osmosis concentrated ammonium salt fertilizer 388 has reduced volume and associated reduced storage, handling, and shipping costs. Additionally, if salt crystals are desired, a forward osmosis membrane crystallizer 399 can be incorporated into the system. Alternatively, thermal evaporation equipment can be used, although at higher capital and energy usage costs.

[0025] The components of the new ammonium salt fertilizer producing system 300 for processing the mechanically filtered biogas digestate 308 includes a treatment tank 342, one or more micro-bubblers or nano-bubblers 346, one or more coagulants 348, one or more flocculants 344, at least one forward osmosis filtration unit 372, an acidic forward osmosis draw solution 374, an input port 376 for adding acid to the diluted forward osmosis draw solution 374a resulting in diluted draw solution 374b, at least one reverse osmosis filtration unit 378, and at least one osmotically assisted reverse osmosis filtration unit 380.38511.0028P1

[0026] The mechanically filtered biogas digestate 308 is temporarily held for treatment in treatment tank 342 and treated with one or more micro-bubblers or nanobubblers 346, one or more coagulants 348, and / or one or more flocculants 344, alone or in combination, to remove contaminants that may impact the performance of at least one downstream forw ard osmosis filtration unit 372. The contaminants include molecules, such as, but not limited to, lignins, mucus, proteins, and protein fragments, that are difficult to mechanically remove and may form gels in the mechanically filtered biogas digestate 308 and in the at least one forward osmosis filtration unit 372. The presence of these gels impacts the ability of the at least one forward osmosis filtration unit 372 to efficiently, effectively, and consistently transfer ammonia across the forward osmosis membranes of the at least one forward osmosis filtration unit 372, and into the forward osmosis draw' solution 374. The presence of these contaminants, if not removed, would challenge the overall viability of the system for cost effectively producing ammonium salt fertilizer 388.

[0027] Coagulants 348 may be used to neutralize charges on particles and flocculants 344 bind the neutralized particles together. Coagulants 348 may include, but are not limited to poly-aluminum chloride, polyamides, or other polymeric coagulants that do not cross the forw ard osmosis membrane.

[0028] There are a wide variety of materials potentially useful for the one or more flocculants 344 such as, but not limited to. polyacrylamide, cellulose, polysaccharides or other polymeric flocculants that do not cross the forward osmosis membrane.

[0029] Since the one or more flocculants 344 and / or coagulants 348 are physically separated from the concentrated ammonium salt fertilizer 388 by the forw ard osmosis filtration unit 372, use of anon-organic certified flocculant for the one or more flocculants 344 and / or use of a non-organic certified coagulant for the one or more coagulants 348 should not impact the organic nature or organic certification of the concentrated ammonium salt fertilizer 388.

[0030] The nano-bubbler or micro-bubbler 346 works in conjunction with the flocculants 344 and / or coagulants 348 to combine and separate the contaminants from the mechanically filtered biogas digestate 308. The materials 352 and 354 containing contaminants combined flocculants, and / or coagulants can be removed from the treatment tank 342 such as by, but not limited to, gravity separation, filtration, and / or vacuum, resulting in the treated biogas effluent 338 remaining in the treatment tank 342.38511.0028P1

[0031] Treated biogas effluent 338 is fed into the at least one forward osmosis filtration unit 372 having acidic draw solution 374 where water and ammonia cross the ammonia-permeable membrane of the forward osmosis filtration unit 372 and this ammonia containing permeate is captured in the acidic draw solution 374 where the ammonia converts to ammonium cations, which have relatively limited permeability back through the forward osmosis membrane of the forward osmosis filtration unit 372. Ammonium ions in the diluted draw solution 374a combined with the acid produces one or more ammonium salts. The diluted draw solution 374a becomes an ammonium brine stream 374b. Biogas effluent is concentrated by at least a factor of 5 and leaves the forward osmosis elements 372 as the flow 336.

[0032] Ammonium brine stream 374b is then fed into the at least one reverse osmosis filtration unit 378, where the ammonium brine stream is dewatered resulting in a clean water permeate 392 and a concentrated retentate ammonium brine stream 374 having a salinity of about 16% in our experiments with ammonium sulfate. Other ammonium salts may have different salinities. Water produced by the reverse osmosis system has salinities less than 250 mg / 1 and leaves the system as flow 392.

[0033] Part of the concentrated ammonium brine stream 374 from the at least one reverse osmosis unit 378 is fed into the at least one osmotically assisted reverse osmosis unit which further dewaters the ammonium brine stream 374 to produce a retentate ammonium salt fertilizer 388 having a salinity of about 33% in our experiments with ammonium sulfate. Other ammonium salts may have different salinities.

[0034] Further concentration to produce ammonium salt cry stals may incorporate a forward osmosis membrane brine cry stallizer 399 into the system to provide an energy efficient alternative and lower capital alternative to thermal evaporation.

Claims

38511.0028P1CLAIMS1. An ammonium salt brine concentration system, the system comprising: a mechanically filtered biogas effluent containing ammonia and containing molecules that have the potential to combine and gel; a treatment tank for treating the mechanically filtered biogas effluent; one or more flocculants and / or coagulants and one or more bubblers used together for treating the mechanically filtered biogas effluent in the treatment tank to combine, capture and separate the molecules from the biogas effluent that have the potential to combine and gel. thus creating a treated biogas effluent containing ammonia; a forward osmosis membrane filtration system comprising at least one forward osmosis membrane in a forward osmosis module having a filter feed portion, a filter retentate portion, a filter permeate portion, and an acidic draw solution that circulates through the filter permeate portion, where the ammonia from the treated biogas effluent is drawn across the forward osmosis membrane and into the draw solution, combining with acid in the acidic draw solution to produce an ammonium salt and thus an ammonium salt brine stream; a reverse osmosis membrane filtration system comprising at least one reverse osmosis membrane in a reverse osmosis module having a filter feed portion, a filter retentate portion, and a filter permeate portion, where the ammonium salt brine stream is fed through the reverse osmosis module, dewatering and concentrating the ammonium salt brine stream; and an osmotically assisted reverse osmosis system comprising at least one osmotically assisted reverse osmosis module having a filter feed portion, a filter retentate portion, and a filter permeate portion, where at least a portion of the ammonium salt brine stream is fed through the osmotically assisted reverse osmosis module, further dewatering and concentrating the ammonium salt brine stream resulting in an ammonium salt fertilizer with a salinity above about 20%.

2. The ammonium salt brine concentration system of claim 1, wherein at least one bubbler of the one or more bubblers is a micro-bubbler.38511.0028P13. The ammonium salt brine concentration system of claim 1, wherein at least one bubbler of the one or more bubblers is a nano-bubbler.

4. The ammonium salt brine concentration system of claim 1, wherein the one or more flocculants and / or coagulants are polymeric, non-organically certified flocculants which are blocked by the forward osmosis membrane.

5. The ammonium salt brine concentration system of claim 1, wherein the potential gel forming molecules includes one or more of lignins, mucus, proteins, or protein fragments.

6. The ammonium salt brine concentration system of claim 1, wherein the ammonium salt fertilizer has a salinity above about 30%.

7. The ammonium salt brine concentration system of claim 1. wherein the concentrated ammonium salt brine stream, the retentate from the osmotically assisted reverse osmosis module, is further concentrated to make ammonium salt crystals.

8. The ammonium salt brine concentration system of claim 7, wherein a forward osmosis membrane crystallizer further concentrates the ammonium salt brine stream to produce the ammonium salt crystals.

9. A treated biogas effluent to be fed to a forw ard osmosis membrane filtration module, the treated effluent comprising: a filtered digester effluent from a biomass digester previously containing molecules that combine and gel causing the forward osmosis membrane filtration module to at least partially clog thereby reducing permeability of the forward osmosis membrane filtration module, wherein the molecules that combine and gel have been at least partially removed from the filtered digester effluent from a biomass digester via a combination of flocculation and / or coagulation and micro-bubbles or nano-bubbles.

10. The treated biogas effluent of claim 9, wherein the potential gel forming molecules includes one or more of lignins, mucus, proteins, or protein fragments.

11. The treated biogas effluent of claim 9, wherein the flocculation and / or coagulation uses a polymeric non-organically certified flocculants and / or coagulants which are blocked by the forward osmosis membrane.

12. A method for producing a concentrated ammonium brine stream, the method comprising: supplying a biogas effluent containing ammonia;38511.0028P1 adding one or more flocculants and / or coagulants to the biogas effluent in a treatment tank, the one or more flocculants and / or coagulants removing potential gel forming molecules from the biogas effluent to create or produce a treated biogas effluent; inputting the treated biogas to the feed side of at least one forward osmosis filter having an acidic draw solution; drawing or transferring ammonia across the forward osmosis filter and into the acidic draw solution; converting the ammonia to ammonium cations and thus creating an ammonium salt brine stream; dewatering the ammonium salt brine stream via reverse osmosis thereby creating a reverse osmosis retentate ammonium salt brine stream; and further concentrating at least a portion of the reverse osmosis retentate ammonium brine stream via osmotically assisted reverse osmosis to produce a concentrated ammonium salt fertilizer with a salinity above 20%.

13. The method of claim 12, wherein a micro-bubbler or nano-bubbler is used in the treatment tank in conjunction with the one or more flocculants and / or coagulants.

14. The method of claim 12, wherein the one or more flocculants and / or coagulants are non-organically certified flocculants and / or coagulants.

15. The method of claim 12, wherein the potential gel forming molecules includes one or more of lignins, mucus, proteins, or protein fragments.

16. The method of claim 12, wherein the concentrated ammonium salt fertilizer has a salinity above about 30%.

17. The method of claim 12, wherein the concentrated ammonium salt brine stream, the retentate from the osmotically assisted reverse osmosis module, is further concentrated to make ammonium salt crystals.

18. The method of claim 17, wherein a forward osmosis membrane crystallizer further concentrates the ammonium salt brine stream to produce the ammonium salt crystals.

19. An organically certified ammonium salt, said ammonium salt produced from biogas effluent where the biogas effluent is treated with non-organic flocculant and / or coagulant; wherein the ammonia in the treated biogas effluent is extracted by a forward osmosis filtration unit thereby eliminating any non-organic materials from the flocculant and / or coagulant from contaminating the final produced ammonium salt.38511.0028P120. An ammonium salt fertilizer production system, where: the system produces ammonium salt fertilizer from mechanically filtered biogas effluent treated with non-organic flocculant and / or non-organic coagulant; the system incorporates at least one forward osmosis filtration unit; and the at least one forw ard osmosis filtration unit prevents any materials from the mechanically filtered biogas effluent treated with non-organic flocculant and / or non- organic coagulant from passing through the at least one forward osmosis filtration unit that would prevent organic certification of the ammonium salt.

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